Fernco or FluidMaster floor seal

Thanks for having such a helpful forum. We are replacing a broken toilet with the Toto UltraMax after laying vinyl over quarter inch plywood. The flange is a bit below the flooring surface and we are trying to decide which type of seal would be easiest, safest to use, double wax, Fernco or the FluidMaster. I did read Terry's instructions for attaching the seal to the toilet rather than the floor. Since it seems they narrow the pipe a little, do the rubber seals have any affect on the flushing action of the toilet? What would you suggest we use.
Thanks
Yankee Senior

The interior trap on most toilets is in the order of 2" or a little over. Some are larger. The diameter of the waxless seals is probably not a restriction. I've had several in for years, and no issues. It would have been best to reset the flange on top of the finished floor where it is supposed to be. You could add an extender ring to bring it up, then use a standard wax ring.

6 Pressed fluidmaster into 4 inch pipe so that seal was about 3/4 inch above floor.

7 Lifted toilet over dowels and set toilet down on seal. The toilet then shoved the seal down to tight fit on top of seal because I used an o-ring with tight fit into drain. No need to use crush paper.
The logic behind this install was that my father in law said all you need to know to be a plumber is that feces and urine stink and water flows down hill.

I checked to see if there was any water leakage by removing one nut on one side of toilet and shoved a dry rag strip into space between horn and edge of toilet came out dry.

Thanks for all the replies and suggestions. Of course we do understand now that the flange should be mounted on the finish floor but it's (the flange) only down a quarter inch from surface and this sounds like the type of situation that the FluidMaster was created for. I think we'll go with that; does the seal have a sticky surface where you press it on the toilet?
yankee senior

I press the Fluidmaster onto the bowl, and then drop the bowl into place.
This way, "I know" the seal is on the bowl.

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After my tile installation, my floor flange is about 3/4 inche below the fisnished floor. I posted on another thread here and one of the suggestions was to use a fernco or a fluidmaster waxless kit. I bought the Fluidmaster 7500 and I was going to follow your installation as seen on the picture above.

I do have a question here: How critical is the fitting of the black O ring on the bottom of the bowl gasket to the pipe. The reason I ask is because the instructions says the O ring should roll into ( inside?) the drain pipe. Since there was the old flange glued into the inside of the pipe, the actual inside diameter maybe off by a little ( less than 3 inches). It is hard enough to try to install the bowl gasket assembly with the thin O ring inside the pipe as instructed on the installation kit. It will be next to impossible to do this if the bowl gasket was installed in the toilet horn first and then lowered into the pipe. The O ring might just slide up the bowl gasket base and not go inside the drain pipe. I don't know if I explained this correctly but hope you guys understand my question. Thanks again.

The weight of the bowl will answer that one.
It' tends to be rather pushy.

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Sorry for my ignorance here but I did not quite understand your reply. So do I need to worry if the O ring does not actually go inside the pipe when I drop the toilet into the flange. BTW, I was using the Drake Toto which I think is similar to the one pictured. Thanks gain for such a quick reply.